Specifications for Mix Seal Surfacing (MSS) Close-Graded Premix Surfacing (CGPS)
2008 Edition

According to IRC SP 78 Clause 3.2.2, aggregates used in Mix Seal Surfacing must meet the grading limits specified in Table 3 of the code. Typical gradation for a 20 mm thick surfacing includes passing percentages at specified sieve sizes to achieve a dense-graded mix. Aggregates should be clean, hard, and durable to ensure adequate wear and skid resistance. The grading range generally includes 100% passing at 20 mm sieve, 85-100% at 14 mm, 60-85% at 10 mm, 30-55% at 4.75 mm, 15-35% at 2.36 mm, 5-20% at 1.18 mm, and 0-10% at 0.6 mm sieve. Variations may be contract-specific. Proper grading ensures a tightly packed aggregate structure essential for durable surfacing.

IRC SP 78 recommends using low-viscosity paving bitumen VG-10 conforming to IS:73, cationic bitumen emulsion RS-1 as per IS:8887/ASTM D2397, and cutback bitumen RC-70 (IS:217) primarily for cold regions or emergencies for tack coat applications. For premix surfacing, viscosity graded paving bitumen according to IS:73 or modified bitumen following IRC:SP:53 should be used. The tack coat binder must be applied uniformly at appropriate temperatures to ensure proper adhesion between layers and achieve a durable 20 mm thick close-graded premix surface.

Per IRC SP 78 Table 5, premix operations require precise temperature control depending on the bitumen grade. For VG-40 bitumen, bitumen temperatures of 160-170°C, aggregate temperatures of 160-175°C, mix discharge at 160-170°C, laying at minimum 150°C, and rolling at minimum 100°C are specified. For VG-30, these ranges are slightly lower, with laying at least 140°C and rolling at 90°C. VG-20 and VG-10 grades require progressively lower temperatures. Modified bitumen needs higher temperatures, with bitumen at 165-185°C and rolling not below 115°C. Rolling must be completed before the mix temperature drops below the specified rolling temperature to ensure adequate compaction and surface integrity.

Surface preparation under IRC SP 78 involves reshaping and conditioning the existing base to a uniform grade and profile, filling and compacting any potholes or depressions, and thoroughly cleaning the surface to remove dust, organic matter, and other contaminants. For granular bases, a prime coat is mandatory before surfacing application to enhance bonding. Ensuring a clean, stable, and correctly profiled base is critical for the successful performance of the 20 mm thick Mix Seal Surfacing layer, especially on roads with low traffic volumes.

Quality control as per IRC SP 78 and IRC:SP:11 involves verifying that aggregates meet physical requirements such as a maximum Los Angeles abrasion value of 40%, soundness losses below prescribed limits, flakiness index under 25%, minimum adhesion retention of 95%, and water absorption not exceeding 1%. Equipment readiness and proper calibration must be ensured. Surface compaction should produce a uniform layer that conforms exactly to design grade and cross-section, with a maximum deviation of 6 mm under a 3-meter straight edge. Continuous monitoring of weather conditions and material temperatures is also essential to maintain construction quality and durability.